An image sensor is a device that converts optical images into electrical signals. With increased development of the computer and communications industries, there may be an increased demand for high performance image sensors that may be used for capturing images in a variety of applications such as digital cameras, camcorders, personal communication systems (PCS's), gaming machines, security cameras, micro-cameras for medical applications, and/or robots.
Image sensors may include complementary metal-oxide-semiconductor (CMOS) image sensors and charge coupled devices (CCDs). CMOS image sensors can be operated with a simple driving manner and may be integrated with signal processing circuits on a single chip, thus enabling products that include the CMOS image sensors to be scaled down. In addition, CMOS image sensors may operate with relatively low power consumption. Thus, CMOS image sensors are applicable to portable electronic devices. Furthermore, CMOS image sensors may be fabricated using CMOS fabrication techniques, which may reduce manufacturing costs. Moreover, CMOS image sensors may provide high resolution images. Accordingly, the use of CMOS image sensors is being increased.
The image sensors may include a plurality of pixel sensors arranged in rows and columns to form a rectangular shape. The pixel sensors in each column may be connected to a corresponding one of column data lines and may be selected row by row to operate the column data lines. Image signals from the column data lines may be converted into digital signals by ADC circuits connected to the column data lines. Various techniques may be used to generate the digital signals from the analogue image signals, including a dual correlated double sampling (dual CDS) using a single-slope analogue-digital converting technique.
The image sensors are being used for portable devices (e.g., cellular phone) or for taking moving pictures, and thus, high resolution, low power consumption, and high speed are needed in the image sensors. Accordingly, a variety of studies are being conducted to reduce a short operation delay that was a negligible issue in the past.